The momentary good audio is likely when the Kia intro sound plays. I have that too.The odd thing is that sometimes when I turn on the car, when I was previously hearing radio, the sound returns to a good quality for a few seconds, goes mute, then craps again.
After I took mine in for troubleshooting it started having a popping sound at startup, like a Taser. That stops after a few seconds.
I noticed the parking and lane change sounds were gone too. That's something to be aware of when backing up.